The goal of this research is to understand the molecular genetic mechanisms controlling the integration of a cell-surface receptor mediated response to a pathogen with the developmental program of the host. Coordination of response to signals with developmental state is essential for the successful and healthy existence of organisms. A disease state may result when the regulation of stage-specific activity is disrupted. Several genetic diseases are caused by these types of malfunctions. The focus is on understanding the developmental control of the disease resistance activity of the receptor-like serine-threonine protein kinase gene Xa21 in rice. Studies focused on developmental control of Xa21-signal transduction will provide important information pertaining to stage- specific control mechanisms and may form the basis for ultimately designing strategies for preventing diseases caused by inappropriate stage-specific activity. The developmental stage is crucial to one or more aspects of the Xa21 signaling pathway or competence to respond. The hypothesis we will test is that Xa21 resistance phenotype is controlled by the developmental program governing the transition from juvenile to adult stages. The three specific aims are designed to comprehensively analyze genes providing developmental regulation of Xa21 resistance and to test three predictions based on the hypothesis: 1.) Genetic and physiological characterization of developmental resistance control factors. Precociously resistant mutants and existing developmental mutant lines will identify developmental control factors; 2.) Construction of mutants in genes that are coordinately expressed or repressed during the transition from susceptibility to resistance. Using antisense and over-expression technologies, varying expression levels of genes that are coordinately expressed or repressed during the transition from susceptible to resistant stage will allow dissection of control of Xa21 resistance phenotype. 3) Global monitoring of gene expression in developmental transition from susceptibility to resistance. Monitoring of global gene expression using cDNA microarray analysis during transition from susceptible stage to resistance stage will allow dissection of regulatory circuitry.